The present application generally relates to printing systems, and more particularly, to identifying faults within printing systems.
Printing systems, which may be referred to as “distributed” or “parallel” or “cluster” printing systems, include several marking engines that are controlled by a control system, which may split a print job among the several marking engines to execute the print job. Each marking engine in the printing system marks print media, e.g., paper, with a marking medium such as ink or toner, where the toner is then fused to the print medium. The marking engines may run at different speeds, print color or monochrome, and/or provide different levels of print quality, where a higher print quality is associated with a higher cost.
In some printing systems, two or more marking engines can each execute a portion of the print job. For example, in duplex printing, one marking engine can print the first side of each sheet of print medium while a second marking engine prints the second side. In simplex printing, two marking engines can print alternate sheets. In some print jobs, e.g., overprinting, two marking engines can apply marking media to the same side of the sheet. A common paper path links two or more marking engines to an output device, such as a finisher, where portions of the executed print job are combined. When a marking engine malfunctions, the control system can reroute the print job, or portion of the print job, while the malfunctioning marking engine is repaired or replaced.
Printing systems with redundant components can provide greater reliability to catastrophic failures of components; however, such redundancy comes at a higher cost of the printing system. In the case of a non-catastrophic failure, a print job can be printed at a lower output speed, or at a higher page cost, or at a lower print quality, depending on the marking engines that are available and operating within acceptable functional parameters, the requirements of other print jobs, and the customer's preferences.
Fault detection results from a binary decision, i.e., either something has gone wrong or everything is fine. Frequently, printing systems rely on fault detection within the individual marking engines. Each marking engine includes sensors that detect and log performance characteristics, such as timing of various events, outputs of feedback control loops, toner properties, voltages and current, developed toner mass on photoreceptors, print quality and registration, color or monochrome values, environmental conditions, actuator values, and the like. A marking engine can detect a fault, which in fact did not originate within the marking engine; instead, the fault may have occurred upstream in the common paper path, for example, in an upstream making engine. Each marking engine reports its detected faults to the control system of the printing system.
Fault identification is a procedure to identify observation values, received from the sensors of the individual marking engines, most relevant to diagnosing a fault. Fault diagnostics is a procedure to determine which fault has occurred, or the cause of the observed value indicating a faulty mode of operation. Fault identification is useful to reconfigure a printing system, so as to operate in the presence of one or more faults, i.e., a fault tolerant system.